Casting for portable communication device

ABSTRACT

The invention relates to a casing for a portable communication device. The casing has an opening face carrying user input elements and a display, and rails are located against movement relative to a spacing element to strengthen the casing against flexing.

FIELD OF THE INVENTION

The invention relates to personal communications devices and housingsfor such devices.

BACKGROUND OF THE INVENTION

Over recent years, personal communications devices ranging from mobilephones to electronic diaries and beyond have moved from being eliteitems to everyday tools. In all these years, however, the designcriteria for the casing for the pieces of equipment have not reallychanged.

Communications devices of this type have casings designed with ease ofassembly, durability, and cost, amongst other things in mind. From thefirst, casings have typically been formed from moulded parts as theselend themselves particularly to automated manufacture and can be easilyautomatically clipped together for assembly. The plastic materials usedare also relatively flexible and consequently resilient against theknocks and drops that will inevitably be encountered by a highlyutilized personal portable device. The design criteria have led tosimilar types of casing being used for all such devices.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention there is provideda casing defining an internal space for accommodating the engine of aportable communication device the casing having an operating face forcarrying user input elements, and comprising a pair of strengtheningmembers located against movement relative to, and separated by, aspacing element, such that the casing is strengthened againstdeflections.

The invention provides a mechanism for strengthening the casing thatwill provide security particularly against longitudinal flexibility,which for a hand held device that is typically longer in longitudinalthan lateral extent can cause problems when brittle materials are usedin forming the casing. This is particularly the case when at least someof the materials from which the casing is formed are not flexible andmay instead be relatively brittle.

By fixing a pair of strengthening members against movement relative tothe spacing element located between them, significant improvement instrength is achieved against flexing or bending in the plane of thespacing element. It also provides some increase in strength againsttwisting. The strength of the assembly is related to the separationdistance. The strength tends to increase with separation distanceprovided the separator has sufficient strength to maintain the relativeposition of the pair of members. By separating the strengtheningmembers, the minimum bend will occur between the two elements increasingthe compression of the member on the inside of the bend and theexpansion of the member on the outside of the bend for any given bend.This will be the effect provided there is no slippage between thestrengthening members and the spacing element. This could occur as aresult of one sliding against the other or one bending away from theother. The connection or connections holding the spacing element againstmovement relative to the pair of strengthening members should be strongenough to maintain the connection across the range of bending forces tobe resisted.

The force necessary to bend a pair fixed against movement relative tothe spacing element is substantially greater than the force required tobend each individually. The whole assembly is stronger because to allowthe assembly to bend the strengthening members will need to stretch orcompress along their length.

The casing will generally have a longitudinal and a lateral extent. Thelongitudinal extent may be significantly greater than its lateralextent. Under these circumstances, to impede longitudinal flexing orbending in the plane of the operating face, the strengthening memberspreferably run parallel to the plane of the operating and rear faces.The pair of strengthening members are then preferably separated in aplane transverse to the plane of the operating face. The plane of thespacing element may define the plane in which flexing of the casing isinhibited.

The strengthening members may be, amongst other things, bars, rods orplates. Elongate strengthening members may extend around part or all ofthe casing. The greater the extent of the strengthening member thegreater the area of the casing protected against bending or flexing.Preferably both long edges of the casing are protected. By providingelongate strengthening members around the full extent of the casing, thecasing is protected against lateral and longitudinal flexing.

If the strengthening members are located on the periphery of the casing,the strengthening members can additionally obscure the edges of housingelements forming the casing from view on the exterior of the assembledhousing.

The strengthening members may be rails that may be continuous, or brokenat discrete points, around the perimeter of the casing. The rails aresuitably sandwiched between respective casing elements and pinned inposition to prevent one sliding over the other. The strengtheningmembers may be attached directly to the separating element or may beattached to other elements of the casing that are fixed relative to theseparating element. The strengthening member, will, in many embodiments,trace the periphery of the casing to strengthen all parts of the casing.Embodiments of the invention can, however, be used to strengthenspecific areas of the casing if desired. Breaks in a rail, for example,tracing the periphery of the casing would then be tolerable.

In embodiments where the housing members comprise a front face, a rearface and a side member for displacing the front and rear faces to createthe internal space, a strengthening member may be located at theintersection between the front face and the side member and/or the sidemember and the rear face. The pair of strengthening members can then bereadily located one on either side of the side member and securedagainst movement relative to the side member.

The casing may be a conventional one part casing or a clamshell, orother two part arrangement, where the user input elements or keys may belocated on a different face to a display. In such two part arrangementsgenerally respective casing portions are fixed such that one is movablerelative to the other. The movement may be rotational or lateral.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described in more detail withreference to FIGS. 1 to 10 of the accompanying drawings of which:

FIG. 1 is a perspective view of a communication device showing oneembodiment of the invention;

FIG. 2 shows front, rear, sides and top views of the communicationdevice of FIG. 1;

FIG. 3 is a schematic representation of a communication device suitablefor embodiments of the present invention;

FIG. 4 is an exploded view of the face of a communication device of oneembodiment of the invention without keys;

FIGS. 5 a and 5 b are sections through the communication device of FIG.1 in the display region;

FIG. 6 is a perspective view of a side frame element and located railsfor constructing a casing

FIGS. 7 a and 7 b are sections through the rails of FIG. 1 showing theconnection to the side casing;

FIGS. 8 a and 8 b are sections through the communication device of FIG.1 in the battery region;

FIG. 9 a longitudinal section through the communication device;

FIG. 10 is a bottom plan view of the device of FIG. 1 (with the chinface protector omitted).

DETAILED DESCRIPTION

The embodiment illustrated in FIG. 1 is a handheld communication device1 with a precious retainable casing 2. The casing 2 of the device hasbeen designed to be customizable to individual taste with preciousmaterials. To enable individual devices to be created, the number ofexternal parts from which the casing is formed is relatively large incontrast to existing communications devices.

The casing 2 has an optically permeable front face 3 providing aseamless transition from a display region 4 to an input region 5 thatincludes a key array 6. The key array 6 includes a first group ofalphanumeric keys 7, for entering telephone numbers, writing textmessages (SMS), writing names (associated with phone numbers), etc. Eachof the twelve alphanumeric keys 7 is provided with a figure “0-9” or asign “#” or “*”, respectively. In an alpha mode each key is associatedwith a number of letters and special signs used in text editing. The keyarray 6 additionally comprises two soft keys 8, 9, two call handlingkeys 10, 11, two scroll keys 12, and an on/off key 13.

The functionality of the soft keys 8, 9 may depend on the state of thecommunication device and position within the menu accessed using thescroll keys 12. The current functionality of the soft keys 8, 9 can beshown in separate fields in the display region 4 just above therespective keys 8, 9.

The two call handling keys 10, 11 are used for establishing a call or aconference call, terminating a call or rejecting an incoming call.

The two direction keys or scroll keys 12, in the handset illustrated areplaced centrally on the front surface of the communication devicebetween the display region 4 and the group of alphanumeric keys 7perform a scrolling function.

The seamless face 3 is formed from an optically seamless light guide 14providing light to illuminate the display region 4 and key legends 15located on the light guide 14 and associated with individual keys of thekey array 6.

The front face 3 is overlaid with a pillow 16 providing apertures 17 tochannel sound from a loud speaker 18 and providing an appropriate feelfor an element of the device that will be located close to the user'sear. The front face 3 is surrounded by a bezel 19 that can be made froma precious metal. This acts to protect the edges of the light guide 14and can help in some embodiments in securing the elements of the casing2 together.

The keys of the key array in this particular embodiment are arranged toprovide particular sensory guidance to the user. Aspects of the designalso allow the light guide 14 to be made from a wide range of materialsincluding those that are brittle and so need to be carefully handled andprotected from shattering.

The casing 2 is formed from the front face 3 surrounded by the bezel 19,a side frame 20 and a back cover 21. The interface between the sideframe 20 and the bezel 19 and the side frame 20 and the rear cover 21are shielded by rails 22, 23 in this embodiment. The rails 22, 23 hideraw edges from view and exposure to ensure that the device 1 is bothlong lasting and elegant. The construction of the casing 2 enables thecasing 2 to be opened with ease to update the engine 24 inside whendesired. The casing 2 is also designed to allow the device toaccommodate different sized and shaped engines 24, which may benecessary through its life.

Other elements of the design will be discussed in greater detail withreference to the later drawings. By way of introduction, the device willbe briefly discussed with reference to its functional elements.

The communication device 1, includes the key array 6, a display 25, anantenna 26, an ear piece speaker 18, a polyphonic speaker 27, and amicrophone 28. The communication device 1 is adapted for communicationvia a wireless telecommunication network, e.g. a wireless network.However, the communication device could also have been designed for acordless network. FIG. 3 shows schematically and functionally elementsof the communication device 1. The microphone 28 records the user'sspeech, and the analogue signals formed thereby are A/D converted by anA/D converter before the speech is encoded in an audio part 29. Theencoded speech signal is transferred to processor 30. The processor 30may support software in the phone. The processor 30 also forms theinterface to peripheral units of the apparatus. These may include aRandom Access Memory (RAM) 31 and a Flash Read. Only Memory (ROM) 32, aSIM card 33, the display 25, and the key array 6, and perhaps a browserapplication 34, and a location module 35.

The browser application 34 can be used to request and receiveinformation from the Internet. The location module 35 enables theterminal 1 to determine its current position.

The processor 30 communicates with a transceiver 36, e.g. a circuit,which is adapted to send and receive messages in a telecommunicationnetwork. The telecommunications network may be a GSM network, but theinvention may also be applied in connection with other networks, such asother kinds of wireless networks and various forms of cordless phonesystems or in dual band phones accessing sets of these systems ornetworks. The audio part 29 speech-decodes the signal, which istransferred from the processor 30 to the earpiece 18 via a D/Aconverter.

The embodiment illustrated in FIG. 1 has a light permeable front face 3that can be formed from sapphire or a similar precious stone. Sapphirehas properties including its scratch resistance and optical clarity thatmake it suitable for use in this context. The light guide provides asuitable external surface to the device. Other materials such as glassor ceramic materials or other minerals and precious stones could,however, also be used in combination with, or instead of, sapphire. Assoon as a mineral such as sapphire is used in place of other moreflexible light permeable materials such as plastics, additional problemsare introduced associated with the characteristics of the material. Indesigning a durable device having, for example, a brittle material for afront piece 3 there are many difficulties, in particular it is useful toincrease the flexibility of the front face and reduce flexing of thefront face.

As can be seen most clearly from FIG. 4, the second layer of thecomposite light guide 51 is made in a number of sections 52-58. Thisenhances flexibility allowing brittle materials to be used for thesecond layer 51. In the embodiment illustrated all brittle parts arebonded to a carrier formed from e.g. plastic or titanium in order tobetter absorb shock. In the embodiment described, the sapphire is formedin individual sections 52-58 for ease of manufacture.

In order to increase the durability of the composite light guide 14 andstrengthen it against damage, the sections 52-58 are adhered to a moreflexible perspex layer 37 that has a cut-out 38 for accommodating theear piece speaker 18 that is optimized for use close to the ear. Thereis another cutout accommodating a light pipe diffuser 39. The sectionsare adhered to the perspex layer 37 leaving gaps 59 extending across theentire width. These gaps 59 act as hinges to allow the composite layer14 to be relatively flexible along its major axis. In the embodimentillustrated, the layout of the key array 6 has been designed with thisin mind. The alphanumeric keys 7 are arranged in groups of threeextending across the whole width of the second layer of the composite51. The function keys or soft key 8, 9 are also arranged in two groupsof three. The soft keys 8, 9 and the top scroll key 12 a follows theline of the alpha numeric keys 7. The call handling keys 10, 11 and thebottom scroll key 12 b, which is displaced from the line of the others,defines the lower edge of one of the elements 57 and the upper edge ofanother of the elements 56. This makes the second row of keys 10, 11, 12b distinctive whilst still avoiding problems in manufacture of theelements 52-58.

Although the embodiment described is designed with a brittle materialsuch as sapphire in mind, the resultant arrangement could be formed fromany number of other materials including plastics that provide therequired optical characteristics. Similarly different key arrangementscould be used without departing from individually inventive conceptsthat are disclosed.

When using a brittle material for a front face light guide 14 problemsare also encountered when connecting the front face 3 to the rest of thecasing elements. In the illustrated embodiment the edges of the brittleelements 52-58 are protected by the bezel 19 that sits around the wholeof the face. The bezel 19, in this embodiment, is formed from a bezelsupport 60 overlaid with a 0.5 mm thick metal sheet, the bezel cover 61.The metal sheet 61 is bonded to the bezel support 60, that may be formedfrom plastic, with an adhesive such as a two part epoxy adhesive or atwo part acrylic adhesive. As the metal sheet 61 is relatively thin thiskeeps the weight of the casing 2 down and also allows relativelyprecious metals such as titanium or gold to be used at relatively lowercost. The bezel 19 could, however, be a single part and/or be formedfrom a single material for example titanium.

The transparent face 3 in this particular embodiment is securely held inplace by a robust mechanism. The perspex layer 37 to which the elements52-58 are bonded extends beyond the area covered by the elements toprovide a lip or edge 62 around the whole of the composite light guide14. This edge 62 is used to secure the front face 3 in position as it istucked under the bezel 19 that defines the perimeter of the front faceand squeezed between the bezel 19 and the side frame 20.

As can be seen in FIG. 1, the bezel 19 is punctuated with front faceprotectors 63 whose function will be described in more detail later.These front face protectors 63, in this particular embodiment play arole in holding the casing elements together.

The front face protectors 63 have a tip part 64 that extends over thebezel 19 and a shaft 65 that passes through the bezel 19 and into theplastic side frame 20. The shaft 65 may be tightened onto the frame 20using a nut 95. In this case the nut stops the front face protectorsfrom falling out of the device. In one embodiment the shafts 65 arescrewed into the tips 64 at one end and into the side frame element 20at the other although other manners of connection could be employed. Theshaft 65 and tip 64 could also be one piece rather than two. The bezel19 and the perspex layer 37 of the transparent face 2 are captured bythe front face protector 63 and side frame element 20 as can be seen inFIG. 8B. The front face protectors 63 accordingly grip the transparentface 3 securely between the side frame 20 and the bezel 19. The frontface protectors 63 are only located next to the key array 6. In order tosecure the transparent face 3 around its perimeter additional screws 66are added to draw the bezel 19 towards the side frame 20 and squeeze thetransparent face 3 in place. In one embodiment, the screws 66 threadthrough the side frame 20 and tap into the bezel support 60. Once thebezel support 60 is secured to the side frame 20 the outer shell 61 ofthe bezel 19 can be adhered to the support 60 to hide the tapped screwends 66. Alternatively the bezel 19 is stuck to the support first (asub-assembly) and this sub-assembly is then screwed to the frame.

As can be seen in the figures, although the more flexible transparentsubstrate 37 is overlaid by the bezel 19 secured in position by thefront face protectors 63 and other connectors, the sapphire ismaintained spaced from the bezel 19 so that it is protected fromchipping or other damage as a result of contact. The edges of thesapphire elements do not protrude above the edge of the bezel 19 toprovide further protection for the more vulnerable edges. In thearrangement described, the transparent face 3 is gripped in positionbetween the bezel 19 and the side frame 20. The more flexible substrate37 could, however receive screws or other fasteners to located itrelative to the other frame members without damaging the more brittlesapphire layer.

To reduce the ingress of dirt or fluids a sealant 69 is located betweenthe bezel 19 and the transparent face 3. One way in which this can beintroduced is to paint a seal on the underside of the bezel 19 whichwhen dry is compressed between the transparent light guide 14 and thebezel 19 when the bezel 19 and the side frame 20 are pulled together.

As can be seen in FIG. 6, 7 or 8, a first rail 22 is located in theinterface between the side frame element 20 and the front face 3. Asecond rail 23 is located between the side frame element 20 and the rearface 21. Each rail is trapped between the side frame and another of thecasing elements to prevent movement relative to the side casing elementin the plane of the side frame. It is also restrained against movementrelative to the side frame along the edge of the frame by pins 99 on thefront and rear casings engaging in apertures 70 in the rail. The railsmade of material substantial enough to suitable strengthen the casingagainst longitudinal flexing, of flexing along the length of the device.By pinning the rails one to either edge of the side frame, the extent towhich compression or extension of the rails needs to occur if the casingis flexed is increased. The centre of the side frame will show theminimum deflection and the top and bottom rails will have acorrespondingly increased extension or compression magnified by thedistance from the centre. By suitably choosing the materials andconstruction of the rails, the connection to the side frame and theproperties in terms of material and separation distance provided by theside frame, the flexibility of the casing can be inhibited to therequired degree.

In addition to providing strength to the casing the form of the rails 22and 23 of this embodiment also hides the discontinuity between thecasing parts from sight and protects vulnerable edges to enhance thedurability of the device 1. The rail 22 may be a stamped metal piece ‘T’shaped in section extending around the perimeter of the side frame 20.The stem of the ‘T’ 68 is trapped between the side frame member 20 andthe bezel 19 as these two pieces are drawn together on assembly. Thestem of the T has apertures 70 that sit over corresponding projections71 on the side frame 20 member to prevent it from being withdrawn frombetween the two parts when in position. The top of the T acts as acarrier plate to which an additional extruded piece 72 is soldered orotherwise adhered to provide a seamless finish. The stem could insteadbe formed from a plastics material in which case an adhesive could beused to attach the extrusion to the stem. In other embodiments, the railcould be formed from a single material. It could be a unitary body or amultiple element member. The shape of the rails is not material providedthey give the desired strength to the casing. The bezel 19 overlayingthe top rail 22, provides additional strength to the rail and thereforeto the casing.

The side frame member 20 in this particular embodiment is a plasticsupport 73 with an exterior cover 74. The cover 74 may again be a metalsheet or perhaps a wood veneer or another layer such as leather. Thebonding agent most suitable for adhering the layer to the plastic framemember 73 will differ depending upon the materials that need to beadhered. For metal to plastic a suitable adhesive is a 2 part epoxyresin or 2 part acrylic adhesive. For metal to metal the adhesive wouldbe a reactive polyurethane film or a two part epoxy resin. Similarly theback cover 21 in this embodiment may have a plastic frame and be coveredwith for example a leather, wood or perhaps metal veneer. With theflexible veneer materials such as leather, it is preferable for thematerial to be taut on the frame. This is achieved during the veneeringprocess using conventional techniques.

The constructed casing 2 provides a housing for the printed circuitboard 50 holding the engine components 24, and a battery 79. When thedevice 1 is a radio telephone, a SIM card holder 80 is provided toaccommodate a SIM card 81. For operation under some radio protocols thiswill clearly not be necessary.

The perspex and sapphire is relatively cold to the touch, the materialof the pillow 16 can be chosen to be a material that inherently warmerto the touch and less prone to marking than a transparent shiny surface.Materials that are thought to be particularly suitable are wood andleather veneers. The shape of the pillow 16 obscures part of the LCD 25,providing opposing triangular sections 82, 83 that are used to indicatebattery capacity and signal strength respectively.

To complete the structure, the casing 2 has a rear cover 21 and internalcompartments 84, 85 suitable for retaining the engine 24 the battery 79and in this embodiment a SIM card 81. The back cover 21 is formed fromthree pieces 96, 97, 98. The device illustrated, in common with manyother radio telephones, advantageously allows access to the batterycompartment 85, as the battery 79 may periodically need replacement. Inorder for the engine 24 to be protected during this activity, thebattery 79 is retained in a compartment providing connectors to theengine 24. Along side the battery compartment 85 in this embodiment isthe SIM card holder 80. Under protocols where a SIM card 81 is used tohold subscription information, the user may wish to remove the SIM card81. For this reason it is convenient for the back cover 21 to beremovable to expose both the battery 79 and the SIM card 81. The batterycompartment 85 and SIM card holder 80 are provided by an internal casingelement 87 that is secured to the side frame 20. This may be formed fromplastic or one of many other suitable materials. In one embodiment thecompartments are formed from stamped metal sheet which may be stainlesssteel.

In the embodiment described the front 3 and rear casing elements 96, 97,98 are secured to the side frame 20. A silicon sealant 69 or similar maybe extruded around the inside of the back cover 21 to prevent unwantedingress of dirt and fluid.

The skilled man will realise that the number of parts. and the manner inwhich they are connected can be changed without departing from theseveral inventive concepts described. For example, in other embodimentsthe casing may be held together using other techniques and in otherways.

As well as obscuring exposed edges, the rails 22, 23 provide additionalelements for customization as they can be formed from a variety ofdifferent materials, in particular different types of precious metal forexample gold or platinum. The weight and cost of the rails can bedetermined by changing the substrate material to be a lightweightmaterial such as plastic if required and providing an extruded ribbonthat bridges the discontinuity and is exposed to view that is made froma more appealing material. The rails could instead be solid metal orother material, or to reduce cost and weight could be hollow or perhapsstamped from one material.

The rails protect vulnerable edges of veneered frames from exposure topotentially damaging forces. In doing this unsightly edges are obscuredfrom view. This provides quality and durability in keeping with theoverall concept of a retainable casing for a communications device.

Aspects of the invention have been discussed with reference to a radiotelephone function. It will be clear to the skilled man that theseaspects apply equally to other portable communications devicessupporting in addition or as an alternative other functions, such as,amongst others electronic diaries, and electronic notepads.

The present invention includes any novel feature or combination offeatures disclosed herein either explicitly or any generalisationthereof irrespective of whether or not it relates to the claimedinvention or mitigates any or all of the problems addressed.

In view of the foregoing description it will be evident to a personskilled in the art that various modifications may be made within thescope of the invention.

1. A casing for a portable communication device, the casing comprising:a first casing element, defining at least a portion of a front operatingface without defining any portion of a rear face, the operating facebeing arranged to carry user input elements; a second casing element,separated from the first casing element, defining at least a portion ofthe rear face without defining any portion of the said front operatingface; and a pair of strengthening members separated by a spacingelement, the strengthening members being positioned between the firstcasing element and the second casing element, and being located againstmovement relative to the spacing element, such that the casing isstrengthened against deflections.
 2. A casing according to claim 1wherein the strengthening members are elongate.
 3. A casing according toclaim 2 wherein the elongate strengthening members extend aroundsubstantially the full extent of the casing.
 4. A casing according toclaim 1 wherein at least one of the pair of strengthening members hasmeans for mating with the spacing element.
 5. A casing according toclaim 1 wherein at least one of the strengthening members extends beyondthe outside of the casing.
 6. A casing according to claim 1 wherein atleast one of the strengthening members obscures an edge of a casingelement forming part of the casing from view on the exterior of thecasing.
 7. A casing according to claim 1 wherein the strengtheningmembers are substantially parallel rails.
 8. A casing according to claim1 wherein the strengthening members are interposed between the first andsecond casing elements.
 9. A casing according to claim 1 wherein thefirst and second casing elements are first and second housing elementsfor forming a housing; and the casing comprises means for locating thehousing elements one relative to another producing, along anintersection between adjacent housing elements, a discontinuity in theexterior of the housing; and wherein at least one of the strengtheningmembers provides means for obscuring an edge of a housing element fromview on the exterior of the assembled housing.
 10. A casing according toclaim 1 wherein the at least one of the pair of strengthening members isseamless along the full extent of at least one edge of a housing.
 11. Acasing according to claim 1 wherein at least one of the pair ofstrengthening members has apertures that sit over correspondingprojections on a spacing element for locating relative thereto.
 12. Aportable communication device comprising a casing according to claim 1.13. A portable communication device according to claim 12 wherein thedevice is a radio telephone.
 14. A casing as claimed in claim 1, whereinthe pair of strengthening members separated by a spacing element arelocated at an intersection between the first and second casing elements.15. A casing as claimed in claim 1, wherein the casing is a hand-heldcasing for a hand-held portable communication device.
 16. A casing asclaimed in claim 1, wherein the pair of strengthening members arefixedly attached to the spacing element.
 17. A casing for a portablecommunication device, the casing comprising: a first casing element,defining at least a portion of a front operating face without definingany portion of a rear face, the operating face being arranged to carryuser input elements; a second casing element, separate from the firstcasing element, defining at least a portion of the rear face withoutdefining any portion of the said front operating face; and a firststrengthening member contacting the first casing element and extendingin a first region positioned between the first casing element and aspacing element, and a second strengthening member contacting the secondcasing element and extending in a second region positioned between thespacing element and the second casing element, the strengthening membersbeing located against movement relative to the spacing element, suchthat the casing is strengthened against deflections.
 18. A casingaccording to claim 17, wherein the first and second strengtheningmembers are elongate.
 19. A casing for a portable communication device,the casing having a length direction, a width direction and a depthdirection, wherein the length is greater than the width and the width isgreater than the depth, the casing comprising: a first casing elementdefining at least a portion of a front operating face without definingany portion of a rear face, the operating face being arranged to carryuser input elements; a second casing element, separate from the firstcasing element, defining at least a portion of the rear face withoutdefining any portion of the said front operating face; first and secondstrengthening members; and a spacing element, wherein the first casingelement and the spacing member are separated in the depth direction bythe first strengthening member, the first strengthening member and thesecond strengthening member are separated in the depth direction by aspacing element and the spacing element and the second casing member areseparated in the depth direction by the second strengthening member. 20.A casing according to claim 19, wherein the pair of strengtheningmembers are elongate and extend along the length of the casing.